feat(channels): make plugin-example package publishable

- Update channel-base to use built dist/ output with proper exports
- Add README with quick start guide and usage instructions
- Add qwen-extension.json manifest for extension discovery
- Add start-server CLI for running the mock WebSocket server
- Update dependencies from local file: to npm version

This enables the plugin-example package to be published and installed
as a standalone extension for testing the channel plugin system.

Co-authored-by: Qwen-Coder <qwen-coder@alibabacloud.com>

packages/channels/plugin-example/README.md

@@ -0,0 +1,97 @@
+# @qwen-code/channel-plugin-example
+
+A reference channel plugin for Qwen Code. It connects to a WebSocket server and routes messages through the full channel pipeline (access control, session routing, agent bridge).
+
+Use this package to:
+
+- **Try out the channel plugin system** — install it as an extension and run it with the built-in mock server
+- **Use it as a starting point** — fork the source to build your own channel adapter (see the [Channel Plugin Developer Guide](../../docs/developers/channel-plugins.md))
+
+## Quick start
+
+### 1. Install the package
+
+```bash
+npm install @qwen-code/channel-plugin-example
+```
+
+### 2. Link it as a Qwen Code extension
+
+The package ships a `qwen-extension.json` manifest, so it works as an extension out of the box:
+
+```bash
+qwen extensions link ./node_modules/@qwen-code/channel-plugin-example
+```
+
+### 3. Configure the channel
+
+Add a channel entry to `~/.qwen/settings.json`:
+
+```json
+{
+  "channels": {
+    "my-plugin-test": {
+      "type": "plugin-example",
+      "serverWsUrl": "ws://localhost:9201",
+      "senderPolicy": "open",
+      "sessionScope": "user",
+      "cwd": "/path/to/your/project"
+    }
+  }
+}
+```
+
+### 4. Start the mock server
+
+```bash
+npx qwen-channel-plugin-example-server
+```
+
+The server prints the HTTP and WebSocket URLs. You can customize ports with environment variables:
+
+```bash
+HTTP_PORT=8080 WS_PORT=8081 npx qwen-channel-plugin-example-server
+```
+
+### 5. Start the channel
+
+In a separate terminal:
+
+```bash
+qwen channel start my-plugin-test
+```
+
+### 6. Send a message
+
+```bash
+curl -sX POST http://localhost:9200/message \
+  -H 'Content-Type: application/json' \
+  -d '{"senderId":"user1","senderName":"Tester","text":"What is 2+2?"}'
+```
+
+You should get a JSON response with the agent's reply.
+
+## How it works
+
+```
+Mock Server (HTTP + WS)
+  ↕ WebSocket
+MockPluginChannel (this package)
+  → Envelope → ChannelBase.handleInbound()
+    → SenderGate → SessionRouter → AcpBridge.prompt()
+      → qwen-code agent → model API
+    ← response
+  ← sendMessage() → WebSocket → Mock Server
+  ← HTTP response
+```
+
+## Building your own channel
+
+See `src/MockPluginChannel.ts` for a working example. The key points:
+
+1. Extend `ChannelBase` and implement `connect()`, `sendMessage()`, `disconnect()`
+2. Build an `Envelope` from incoming platform messages and call `this.handleInbound(envelope)`
+3. Export a `plugin` object conforming to `ChannelPlugin`
+4. Add a `qwen-extension.json` manifest
+
+Full guide: [Channel Plugin Developer Guide](../../docs/developers/channel-plugins.md)